1. Field of the Invention
The present invention relates to a preferable fluorescent lamp in which after formation of a phosphor layer, a glass bulb is heated and softened so as to be bent and molded, and an illuminating apparatus having the same.
2. Description of the Related Art
Japanese Patent No. 3055769 describes a straight tube-shaped, annular, or single-base-type fluorescent lamp known as a common illuminating fluorescent lamp, and in particular, a small-diameter annular fluorescent lamp dedicated to high-frequency lighting and which meets recent requirements for energy and resource saving. This small-diameter annular fluorescent lamp is identified by the commercial model name “FHC”. Compared to conventional annular fluorescent lamps, the small-diameter annular fluorescent lamp has almost the same annular outer diameter but can offer a reduced outer tube diameter and a comparable or improved lamp efficiency or brightness. The small-diameter annular fluorescent lamp can thus meet the needs for energy and resource saving, and in particular, provides a comfortable visual environment in a residential space.
On the other hand, Japanese Patent Laid-Open No. 58-152365 describes a rectangular fluorescent lamp. This 30-W type rectangular fluorescent lamp uses a square bulb having an outer tube diameter of 25 to 32 mm, a radius of curvature of 20 to 40 mm inside its bent part, and an outer dimension of 190 to 220 mm between opposite straight parts. Another rectangular fluorescent lamp is known which is of a 32-W type and which has an outer dimension of 260 to 290 mm between the opposite straight parts.
Blackening of the glass caused by implantation of mercury can be suppressed by, in forming a fluorescent layer on an inner surface of the fluorescent lamp, forming a protective film before forming a fluorescent layer on an inner surface of the protective film. The protective film is commonly formed by applying an applicator of fine grains such as γ-Al2O3 to the inner surface of the glass bulb, drying the applicator, and heating and sintering the glass bulb. If the fluorescent lamp is bent, the step of forming a protective film and a phosphor layer and the step of molding a glass bulb have an arbitrary sequential relationship; molding of a glass bulb as described above may precede or follow formation of a protective film and a phosphor layer. However, for a small-diameter fluorescent lamp shaped like a rectangle or the like, forming a protective film and a phosphor layer before molding a glass bulb is suitable for mass production.
Japanese Patent Laid-Open No. 2004-006185 describes a technique for using strontium phosphate (Sr2P2O7) fine grains with a relatively large grain size as a material for a protective film in order to reduce the amount of fluorophor used in the fluorescent lamp.
However, it has been known that when a fluorescent lamp having small-diameter bent parts with a small radius of curvature such as corners of a rectangle is manufactured on the basis of the prior art, the phosphor layer in the bent part is prone to be cracked or peeled off. This may disadvantageously degrade the appearance of the fluorescent lamp. On the basis of their examinations, the present inventors assume that if the glass bulb is molded by heating and softening it and when the glass in the bent portions is shrunk, the protective film is not shrunk accordingly. The protective film shown in Japanese Patent Laid-Open No. 2004-006185 has not been sufficiently examined for the relationship between cracking of the phosphor layer which may occur during formation of bent parts and the configuration of the protective film.